Coaxial Al4C3/Al2O3@Cf composite with tunable core–shell architecture for synergistic electromagnetic absorption and thermal insulation

Impedance mismatch and high-temperature oxidation are two main factors that limit the practical application of carbon-based absorbing materials. Although micro/nano-structured composites have been explored to alleviate these issues, they often suffer from dispersion instability and structural fragility. In this work, a coaxial composite fiber microwave absorber (Al 4 C 3 /Al 2 O 3 @C f ) is fabricated using carbon fiber (C f ) as a template and conductive core, with an Al 4 C 3 /Al 2 O 3 ceramic shell grown in situ via a vapor–solid reaction. Compared to pristine C f , which exhibits negligible absorption, the optimized composite achieves a minimum reflection loss of −49.27 dB, attributed to interfacial polarization and a built-in capacitor-like structure. Meanwhile, the material also features excellent oxidation resistance and thermal insulation (0.0567 W m −1  K −1 at 100 °C). This study presents a structurally controllable, thermally robust absorber design that overcomes key limitations of traditional carbon-based materials, offering a promising solution for next-generation electromagnetic protection in aerospace and harsh environments.